This invention relates to a high-frequency heating generator comprising an electron tube oscillator circuit, an electron-tube grid being connected to a positive feedback circuit of the oscillator circuit, and an electron tube anode being connected to a d.c. power source.
The present invention more specifically relates to high-frequency generators for industrial systems ranging from several kilowatts to a number of megawatts. High-frequency generators now being applied in industry are exclusively operated with the conventional usual triodes as an electron tube. Despite the fact that there are tetrodes on the market, they are not used in high-frequency or inductive heating generators, as for comparable power values it is considerably less expensive to incorporate triodes rather than tetrodes in the high-frequency generator.
The present invention is based on the idea that for a balanced cost analysis the entire high-frequency generator should be considered and not only the oscillator circuit.
Highly efficient power control of a triode requires a thyristor controller which can only be implemented in a simple manner for voltages up to 500 volts. However, for highly efficient use the triodes are required to operate at 10-50 kilovolts, making it necessary to incorporate a high-voltage transformer after the thyristor controller.
As a result of the use of a thyristor controller, the cost of the known high-frequency generator is not only higher than it would be if a thyristor controller could be dispensed with, but, in addition, in industrial systems the thyristor controller mostly requires a filter at the output of the high-voltage rectifier, which filter is not only costly but also voluminous due to the high voltage occurring there. In this connection, it should be observed that the production of plasma inevitably requires the use of a filter of this type as otherwise power variations in a plasma flame would cause a deafening noise.